Oil seed rape: the oil crop that turns the countryside yellow

England is sometimes referred to as a green and pleasant land, but if you travel around the country during April and May you are likely to see large areas where it has turned yellow. This is due to the flowering of the crop plant oil seed rape (Brassica napus).

Oil seed rape, also known as rapeseed or canola, belongs to the same plant family as the humble cabbage. Its seeds are harvested and processed to produce oil for cooking and biodiesel, along with a protein-rich by-product used for animal feed. Oil seed rape is the third largest source of vegetable oil behind palm and soybean (1). Around 4 million metric tonnes of oilseed were produced in 2012 (2), with production look set to rise in future. The World’s leading producers of oil seed rape are Europe, Canada, USA, Australia, China and India. Rapeseed oil is the oil of choice for biodiesel production in most of Europe. This is because oil seed rape produces more oil per unit of land than other oil sources, but also because rapeseed oil freezes at a lower temperature than most other vegetable oils.

Oil seed rape also contributes to honey production as its flowers are pollinated by bees. Honey made from oil seed rape nectar is quick to crystallize and produces a set honey with a fine texture.

The increasing demand for oil seed rape is driving a desire to reduce crop losses through environmental stresses or from infection by disease-causing microbes. One of the most devastating diseases is called white stem rot. It is caused infection of the fungus Sclerotinia sclerotiorum, which leads to rotting of leaves, stems and pods (2). This results in significant losses of seeds, which in severe cases in China have been recorded to be as high as 80% of the expected yields (2).

There is little natural resistance in oil seed rape varieties, so there aren’t many opportunities to use conventional breeding to produce more resistant varieties. Instead, disease control heavily relies on the use of fungicides. Not only is this bad for the environment, it also increases the cost of growing the crop. Also, fungicide treatment is not always very effective because when sprayed over the crop it may not penetrate the dense canopy to reach the stems below.

Few genes involved in the oil seed rape and S. sclerotiorum interaction have been identified. In a recent paper published in Molecular Plant Pathology, scientists found that oil seed rape lines that overexpressed a gene called WRKY33 had increased resistance to S. sclerotiorum infection (2). WRKY33 encodes a transcription factor protein, meaning that it can regulate other genes to turn on or off the production of certain proteins. WRKY33 was found to interact with two other proteins, providing some clues as to how WRKY33 may be activated during plant defence. The genes that encode WRKY33 and its interacting proteins are potential candidates to to make genetically modified oil seed rape varieties with increased resistance to S.sclerotiorum infection.